RESEARCH GOAL FOR THE COMING YEAR: In keeping with the original grant proposal, our basic goals for this coming year will be the following: (a) Investigate the chemical identity of the radioimmunoassayable fraction of T3 and T4 found in milk to native T3 and T4. The greatest amount of time will be devoted to this section. Using the "Methods of Procedure" outlined in the original grant proposal, we will attempt to radiolabel the "carrier" moiety in vivo, using rats injected with 125I. Once we are able to follow the tagged "carrier" moiety, we will direct our attention to its isolation and purification, using biochemical techniques appropriate to the nature of the substance (i.e., protein, lipid, etc.). (b) Investigate the nature of the "carrier" moiety and its biological effectiveness. To continue, on an expanded scale, the investigaions of the biological effectiveness of the T3 and T4-like radioimmunoassayable material extracted from human milk. The investigations will employ a methodology similar to that described in Section (a) of the "Description of Studies Conducted This Year". (c) Establish normal values of milk T3 and T4 with respect to the post-partum period of lactation. Once the nature of the "carrier" substance has been determined, we will be better able to accurately quantitate the concentrations of the T3-T4-like substance in human milk, by proceduues which will entail dissociation of the "carrier" moiety from the radioimmunoassayable hormone-like material.